Expandable preformed structures for deployment in interior body regions

ABSTRACT

A tool for deploying an expandable structure into interior body regions provides a catheter body having an interior lumen. The catheter body carries an expandable structure. A stylet is sized configured for passage through the lumen and adapted to straighten the expandable structure during deployment into an interior body region.

RELATED APPLICATIONS

[0001] This application is a divisional of copending U.S. patentapplication Ser. No. 09/420,529, filed Oct. 19, 1999, which is acontinuation-in-part of U.S. patent application Ser. No. 09/088,459,filed Jun. 1, 1998, and entitled “Expandable Preformed Structures forDeployment in Interior Body Regions,” now abandoned.

FIELD OF THE INVENTION

[0002] The invention relates to expandable structures, which, in use,are deployed in interior body regions of humans and other animals.

BACKGROUND OF THE INVENTION

[0003] The deployment of expandable structures, generically called“balloons,” into cancellous bone is known. For example, U.S. Pat. Nos.4,969,888 and 5,108,404 disclose apparatus and methods using expandablestructures in cancellous bone for the fixation of fractures or otherosteoporotic and non-osteoporotic conditions of human and animal bones.

SUMMARY OF THE INVENTION

[0004] According to one aspect of the invention, a tool for deploying anexpandable structure into bone comprises a catheter body defining aninterior lumen and having a proximal end and a distal end. An expandablestructure having a distal end is carried by the catheter body. A stylethaving a proximal end is sized and configured for passage through thelumen and adapted to straighten the expandable structure duringdeployment into an interior body region.

[0005] In one embodiment, the stylet is substantially rigid. In oneembodiment, the stylet is made of stainless steel.

[0006] According to another aspect of the invention, the proximal end ofthe stylet is coupleable to the catheter body after passage of thestylet through the lumen.

[0007] According to yet another aspect of the invention, the styletabuts against the distal end of the expandable structure after passageof the stylet through the lumen.

[0008] Features and advantages of the inventions are set forth in thefollowing Description and Drawings, as well as in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a coronal view of a vertebral body;

[0010]FIG. 2 is a lateral view of the vertebral body shown in FIG. 1;

[0011]FIG. 3 is a plan view of a tool which carries at its distal end anexpandable structure that embodies features of the invention;

[0012]FIG. 4 is an enlarged view of the proximal end of the tool shownin FIG. 3, showing the handle and connected luer fittings;

[0013]FIG. 5 is an enlarged view of the distal end of the tool shown inFIG. 3, showing the expandable structure;

[0014]FIG. 6 is a plan view of the tool shown in FIG. 3, also showing astylet that can be inserted into the tool to straighten the expandablestructure during deployment in bone;

[0015]FIG. 7 is an enlarged view of the distal end of the tool shown inFIG. 3, also showing an insertion sleeve that can be used to compact theexpandable structure prior to insertion into a cannula;

[0016]FIG. 8 is a top view of a mold forming the expandable structureshown in FIG. 5;

[0017]FIG. 9 is a coronal view of the vertebral body shown in FIG. 1,with the tool shown in FIG. 3 deployed to compress cancellous bone as aresult of inflating the expandable structure;

[0018]FIG. 10 is a coronal view of the vertebral body shown in FIG. 9,upon removal of the tool, showing the cavity formed by the compressionof cancellous bone by the expandable structure;

[0019]FIG. 11 is an enlarged view of the expandable structure shown inFIG. 5, diagrammatically showing the expansion characteristics of thestructure; and

[0020]FIG. 12 is a graph which plots the effects of increasing pressureapplied to the interior of the structure to the expanded volume of thestructure.

[0021] The invention may be embodied in several forms without departingfrom its spirit or essential characteristics. The scope of the inventionis defined in the appended claims, rather than in the specificdescription preceding them. All embodiments that fall within the meaningand range of equivalency of the claims are therefore intended to beembraced by the claims.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0022] The preferred embodiment describes improved systems and methodsthat embody features of the invention in the context of treating bones.This is because the new systems and methods are advantageous when usedfor this purpose. However, aspects of the invention can beadvantageously applied for diagnostic or therapeutic purposes in otherareas of the body.

[0023] The new systems and methods will be more specifically describedin the context of the treatment of human vertebra. Of course, otherhuman or animal bone types can be treated in the same or equivalentfashion.

[0024] I. Anatomy of a Vertebral Body

[0025]FIG. 1 shows a coronal (top) view of a human lumbar vertebra 12.FIG. 2 shows a lateral (side) view of the vertebra 12. The vertebra 12includes a vertebral body 26, which extends on the anterior (i.e., frontor chest) side of the vertebra 12. The vertebral body 26 is shapedgenerally like a marshmallow.

[0026] As FIGS. 1 and 2 show, the vertebral body 26 includes an exteriorformed from compact cortical bone 28. The cortical bone 28 encloses aninterior volume of reticulated cancellous, or spongy, bone 32 (alsocalled medullary bone or trabecular bone).

[0027] The spinal canal 36 (see FIG. 1), is located on the posterior(i.e., back) side of each vertebra 12. The spinal cord (not shown)passes through the spinal canal 36. The vertebral arch 40 surrounds thespinal canal 36. Left and right pedicles 42 of the vertebral arch 40adjoin the vertebral body 26. The spinous process 44 extends from theposterior of the vertebral arch 40, as do the left and right transverseprocesses 46.

[0028] It may be indicated, due to disease or trauma, to compresscancellous bone within the vertebral body. The compression, for example,can be used to form an interior cavity, which receives a fillingmaterial, e.g., a flowable material that sets to a hardened condition,like bone cement, allograft tissue, autograft tissue, hydroxyapatite, orsynthetic bone substitute, as well as a medication, or combinationsthereof, to provide improved interior support for cortical bone or othertherapeutic functions, or both. The compaction of cancellous bone alsoexerts interior force upon cortical bone, making it possible to elevateor push broken and compressed bone back to or near its originalprefracture, or other desired, condition.

[0029] II. Tool for Treating Vertebral Bodies

[0030] FIGS. 3 to 5 show a tool 48 for accessing bone for the purpose ofcompacting cancellous bone. The tool 48 includes a catheter tubeassembly 10. The distal end of the catheter tube assembly 10 carries anexpandable structure 56. In use, the structure is deployed and expandedinside bone, e.g., in the vertebral body 26 shown in FIGS. 1 and 2, tocompact cancellous bone 32, as will be described later.

[0031] As best shown in FIGS. 4 and 5, the catheter tube assembly 10includes an outer catheter body 16 and an inner catheter body 18, whichextends through the outer catheter body 16. The proximal ends of theouter and inner catheter bodies 16 and 18 are coupled to a y-shapedadaptor/handle 14 (as FIG. 4 shows).

[0032] As FIG. 5 shows, the expandable structure 56 is coupled at itsproximal end to the distal end of the outer catheter body 16. Likewise,the expandable structure is coupled at its distal end to the distal endof the inner catheter body 18.

[0033] The outer catheter body 16 defines an interior lumen 20 (seeFIGS. 4 and 5), through which the inner catheter body 18 extends. Inuse, the interior lumen 20 conveys a pressurized liquid, e.g., sterilewater, radiopaque fluid (such as CONRAY™ solution, from Mallinkrodt,Inc., or another fluid into the structure 56, to expand it.

[0034] A first female-to-male luer fitting 22 is secured to the handle14 and serves, in use, to couple the interior lumen 20 to a source ofpressured liquid.

[0035] As FIGS. 4 and 5 also show, the inner catheter body 18 defines aninterior lumen 24, which passes concentrically through the interiorlumen 20 of the outer catheter body 16. In use, the interior lumen 24can serve to convey a flushing liquid, e.g., sterile saline, fordischarge through an opening 30 at the distal end of the inner catheterbody 18.

[0036] A second female-to-male luer fitting 34, which is joined to theinner catheter body 18, is also secured to the handle 14. If desired,the second female-to-male luer fitting 34 can serve to couple theinterior lumen 24 to a source of flushing liquid. In addition, theinterior lumen 24 of the inner catheter body 18 can accommodate passageof a stylet 38 (see FIG. 6). The distal end of the stylet 38 ispreferably radiused, to prevent puncture of the inner catheter body 18.

[0037] As FIG. 6 shows, the stylet 38 desirably carries a screw cap 50,which when attached to the second luer fitting 34, holds the stylet 38in place within the inner catheter body 18. In the illustratedembodiment, the proximal end of the inner catheter body 18 includes aflared region 52 (see FIG. 4) where it joins the second luer fitting 34.The flared region 52 allows smooth insertion of the stylet 38, free ofinterference or contact with the peripheral edge of the inner catheterbody 18.

[0038] When the cap 50 is screwed into the second luer fitting 34, thestylet 38 desirably extends through the entire interior lumen 24 of theinner catheter body 18. In the illustrated embodiment, the opening 30 atthe distal end of the inner catheter body 18 is sized to block passageof the stylet 38 beyond the distal end of the inner catheter body 18.Thus, when inserted through the interior lumen 24 and locked to thehandle 14 with the screw cap 50, the stylet 38 desirably abuts againstthe distal end of the structure 56. The presence of the stylet 38desirably prevents the structure 56 from bunching or deflecting when thestructure 56 is inserted into the cannula 78 and/or bone.

[0039] The tool 48 also includes an insertion sleeve 54 (see FIG. 7).The insertion sleeve 54 is carried for sliding movement along the outercatheter body 16. The insertion sleeve 54 slides forward over thestructure 56 (shown in phantom lines in FIG. 7), to protect and compressthe structure 56 during its insertion into the cannula 78. Once thestructure 56 is deployed into the cannula 78, the insertion sleeve 54slides aft away from the structure 56 (shown in solid lines in FIG. 7),and can, if desired, engage the handle 14.

[0040] Various materials can be selected for the component parts of thetool 48. Furthermore, the dimensions of the component parts of the tool48 can also vary, according to its intended use. The following tablelists preferred component materials and dimensions, which are wellsuited for a tool 48 that can be deployed for use in a vertebral body:Component Material Dimension (Inches) Outer 99% TEXIN ® 5270 OutsideDiameter: catheter Polyurethane 0.102 body 16 1% Titanium InsideDiameter: Dioxide 0.078 (Colorant) Inner A Blend Outside Diameter:catheter Comprising: 0.063 body 18 25% TEXIN ® 5286 Polyurethane InsideDiameter: 75% TEXIN ® 5270 0.043 Polyurethane Expandable TEXIN ® 5286 AsFormed: Structure Polyurethane Axial Length (From Distal End of OuterCatheter Tube to Distal end of Inner Catheter Tube): 0.949 CompressedDiameter: 0.160″ Non - Expanded Diameter: 0.270″ Tool Total End to EndLength: 15.75 Stylet Stainless Steel Outside Diameter: 0.038 InsertionPEBAX ® Tubing Outside Diameter: sleeve 54 0.195 Inside Diameter: 0.160Length: 1.5

[0041] The blend of polyurethane materials for the inner catheter body18 desirably enhances the strength of the distal bond between the innercatheter body 18 and the structure 56, due to the presence in bothcomponents of the common TEXIN® 5286 Polyurethane material. Thisimproved bond allows the length of the distal bond to be reduced withoutsacrificing bond integrity. In addition, because both the inner catheterbody 18 and the structure 56 are clear plastic, visual inspection of thedistal bond area is simplified.

[0042] The component parts of the tool 48 can be formed and assembled invarious ways. A preferred assembly will now be described.

[0043] A. The Expandable Structure

[0044] The material from which the structure 56 is made should possessvarious physical and mechanical properties to optimize its functionalcapabilities to compact cancellous bone. The three most importantproperties are the ability to expand its volume; the ability to deformin a desired way when expanding and assume a desired shape inside bone;and the ability to withstand abrasion, tearing, and puncture when incontact with cancellous bone.

[0045] 1. Expansion Property

[0046] A first desired property for the structure material is theability to expand or otherwise increase its volume without failure. Thisproperty enables the structure 56 to be deployed in a collapsed, lowprofile condition subcutaneously, e.g., through a cannula, into thetargeted bone region. This property also enables the expansion of thestructure 56 inside the targeted bone region to press against andcompress surrounding cancellous bone, or move cortical bone to aprefracture or other desired condition, or both.

[0047] The desired expansion property for the structure material can becharacterized by ultimate elongation properties, which indicate thedegree of expansion that the material can accommodate prior to failure.Sufficient ultimate elongation permits the structure 56 to compactcortical bone, as well as lift contiguous cortical bone, if necessary,prior to wall failure. Desirably, the structure 56 will comprisematerial able to undergo an ultimate elongation of at least 50%, priorto wall failure when expanded outside of bone. More desirably, thestructure will comprise material able to undergo an ultimate elongationof at least 150%, prior to wall failure, when expanded outside of bone.Most desirably, the structure will comprise material able to undergo anultimate elongation of at least 300%, prior to wall failure, whenexpanded outside of bone.

[0048] 2. Shape Property

[0049] A second desired property for the material of the structure 56 isthe ability to predictably deform during expansion, so that thestructure 56 consistently achieves a desired shape inside bone.

[0050] The shape of the structure 56, when expanded in bone, isdesirably selected by the physician, taking into account the morphologyand geometry of the site to be treated. The shape of the cancellous boneto be compressed, and the local structures that could be harmed if bonewere moved inappropriately, are generally understood by medicalprofessionals using textbooks of human skeletal anatomy along with theirknowledge of the site and its disease or injury, and also taking intoaccount the teachings of U.S. patent application Ser. No. 08/788,786,filed Jan. 23, 1997, and entitled “Improved Inflatable Device for Use inSurgical Protocol Relating to Fixation of Bone,” which is incorporatedherein by reference. The physician is also desirably able to select thedesired expanded shape inside bone based upon prior analysis of themorphology of the targeted bone using, for example, plain film x-ray,fluoroscopic x-ray, or MRI or CT scanning. The expanded shape insidebone is selected to optimize the formation of a cavity that, when filledwith a selected material, provides support across the region of the bonebeing treated. The selected expanded shape is made by evaluation of thepredicted deformation that will occur with increased volume due to theshape and physiology of the targeted bone region.

[0051] In some instances, it is desirable, when creating a cavity, toalso move or displace the cortical bone to achieve the desiredtherapeutic result. Such movement is not per se harmful, as that term isused in this Specification, because it is indicated to achieve thedesired therapeutic result. By definition, harm results when expansionof the structure 56 results in a worsening of the overall condition ofthe bone and surrounding anatomic structures, for example, by injury tosurrounding tissue or causing a permanent adverse change in bonebiomechanics.

[0052] As one general consideration, in cases where the bone diseasecausing fracture (or the risk of fracture) is the loss of cancellousbone mass (as in osteoporosis), the selection of the expanded shape ofthe structure 56 inside bone should take into account the cancellousbone volume which should be compacted to achieve the desired therapeuticresult. An exemplary range is about 30% to 90% of the cancellous bonevolume, but the range can vary depending upon the targeted bone region.Generally speaking, compacting less of the cancellous bone volume leavesmore uncompacted, diseased cancellous bone at the treatment site.

[0053] Another general guideline for the selection of the expanded shapeof the structure 56 inside bone is the amount that the targetedfractured bone region has been displaced or depressed. The controlleddeformation diameter expansion of the structure 56 within the cancellousbone region inside a bone can elevate or push the fractured corticalwall back to or near its anatomic position occupied before fractureoccurred. Generally speaking, inadequate compaction of cancellous boneresults in less lifting of contiguous cortical bone.

[0054] For practical reasons, it is desired that the expanded shape ofthe structure 56 inside bone, when in contact with cancellous bone,substantially conforms to the shape of the structure 56 outside bone,when in an open air environment. This allows the physician to select inan open air environment a structure having an expanded shape desired tomeet the targeted therapeutic result, with the confidence that theexpanded shape inside bone will be similar in important respects.

[0055] An optimal degree of shaping can be achieved by materialselection and by special manufacturing techniques, e.g., thermoformingor blow molding, as will be described in greater detail later.

[0056] 3. Toughness Property

[0057] A third desired property for the structure 56 is the ability toresist surface abrasion, tearing, and puncture when in contact withcancellous bone. This property can be characterized in various ways.

[0058] One way of measuring a material's resistance to abrasion, tearingand/or puncture is by a Taber Abrasion test. A Taber Abrasion testevaluates the resistance of a material to abrasive wear. For example, ina Taber Abrasion test configured with an H-18 abrasive wheel and a 1 kgload for 1000 cycles (ASTM Test Method D 3489), Texin® 5270 materialexhibits a Taber Abrasion value of approximately 75 mg loss. As anotherexample, under the same conditions Texin® 5286 material exhibits a TaberAbrasion value of approximately 30 mg loss. Typically, a lower TaberAbrasion value indicates a greater resistance to abrasion. Desirably,the structure will comprise material having a Taber Abrasion value underthese conditions of less than approximately 200 mg loss. More desirably,the structure will comprise material having a Taber Abrasion value underthese conditions of less than approximately 145 mg loss. Most desirably,the structure will comprise material having a Taber Abrasion value underthese conditions of less than approximately 90 mg loss.

[0059] Another way of measuring a material's resistance to abrasion,tearing and/or puncture is by Elmendorf Tear Strength. For example,under ASTM Test Method D 624, Texin® 5270 material exhibits a TearStrength of 1,100 lb-ft/in. As another example, under the sameconditions, Texin 5286 exhibits a Tear Strength of 500 lb-ft/in.Typically, a higher Tear Strength indicates a greater resistance totearing. Desirably, the structure will comprise material having a TearStrength under these conditions of at least approximately 150 lb-ft/in.More desirably, the structure will comprise material having a TearStrength under these conditions of at least approximately 220 lb-ft/in.Most desirably, the structure will comprise material having a TearStrength under these conditions of at least approximately 280 lb-ft/in.

[0060] Another way of measuring a material's resistance to abrasion,tearing and/or puncture is by Shore Hardness. For example, under ASTMTest Method D 2240, Texin® 5270 material exhibits a Shore Hardness of70D. As another example, under the same conditions, Texin® 5286 materialexhibits a Shore Hardness of 86A. Typically, a lower Shore Hardnessnumber on a given scale indicates a greater degree of elasticity,flexibility and ductility. Desirably, the structure will comprisematerial having a Shore Hardness under these conditions of less thanapproximately 75D. More desirably, the structure will comprise materialhaving a Shore Hardness under these conditions of less thanapproximately 65D. Most desirably, the structure will comprise materialhaving a Shore Hardness under these conditions of less thanapproximately 10A.

[0061] It should be noted that a structure incorporating a plurality ofmaterials, such as layered materials and/or composites, may possesssignificant resistance to surface abrasion, tearing and puncture. Forexample, a layered expandable structure incorporating an inner bodyformed of material having a Taber Abrasion value of greater than 200 mgloss and an outer body having a shore hardness of greater than 75D mightpossess significant resistance to surface abrasion, tearing andpuncture. Similarly, other combinations of materials could possess thedesired toughness to accomplish the desired goal of compressingcancellous bone and/or moving cortical bone prior to material failure.

[0062] 4. Creating a Pre-Formed Structure

[0063] The expansion and shape properties just described can be enhancedand further optimized for compacting cancellous bone by selecting anelastomer material, which also possess the capability of beingpreformed, i.e., to acquire a desired shape by exposure, e.g., to heatand pressure, e.g., through the use of conventional thermoforming orblow molding techniques. Candidate materials that meet this criteriainclude polyurethane, silicone, thermoplastic rubber, nylon, andthermoplastic elastomer materials.

[0064] As described earlier, in the illustrated embodiment, TEXIN® 5286polyurethane material is used. This material is commercially availablefrom Bayer in pellet form.

[0065] The pellets can be processed and extruded in a tubular shapeusing, e.g., a screw type (888 4:1) extrusion machine, with a GENCA™head, with a single finger spider and a 80-100-200 screen. The followingtable summarizes representative process settings for the extrusion.Extrusion Element Nominal Setting Die 0.338″ Mandrel 0.180″ Zone 1Set/Actual 270 degrees F. Zone 2 Set/Actual 370 degrees F. Zone 3Set/Actual 380 degrees F. Melt Temperature 405 degrees F. ClampSet/Actual 370 degrees F. Adaptor Set/Actual 380 degrees F. Die 1Set/Actual 380 degrees F. Die 2 Set/Actual 380 degrees F. Extruder 1600RPM Barrel 1600 PSI Motor 5 Amps Mandrel Air 2″ of water Entry HoleDiameter 0.3″ Bath Dist. from Tooling 1″ Water Flow/Temperature 6 GPH/70degrees F. Air Wipe 20 PSI Speed 21.5 FPM Min Dryer Time/TemperatureOvernight/160 degrees F.

[0066] The ultimate dimensions of the tubular extrusion can vary,according to the desired size and shape of the structure 56. In arepresentative embodiment, the tubular extrusion has an outside diameterof 0.164″, and inner diameter of 0.092″, and a wall diameter of 0.36″.Reasonable processing tolerances can of course be established

[0067] The tubular extrusion is cut into individual lengths for furtherprocessing. The tube length can vary, according to the desiredconfiguration of the structure 56. In a representative embodiment, eachtube is cut to a length of about 48″ for further processing.

[0068] The structure 56 is formed by exposing a cut tube length 60 toheat and then enclosing the heated tube 60 within a mold 58 whilepositive interior pressure is applied to the tube length 60. The mold 10can be part of a conventional balloon forming machine, such as the ModelNo. 9608C made by Interface Associates.

[0069] As FIG. 8 shows, the mold 58 includes a tube holding channel 62,through which the tube length 60 extends for processing. The holdingchannel 62 includes a formed intermediate cavity 64, which possesses adesired geometry. The cavity 64 defines the geometry intended for thestructure 56.

[0070] In the illustrated embodiment, the cavity 64 possesses twoenlarged cavity spaces 92 and 94 with an intermediate channel 96. Thedimensions of the spaces 92, 94 and channel 96 can, of course, varyaccording to the desired dimensions of the structure 56.

[0071] In a representative embodiment, each enlarged cavity space 92 and94 extends 0.395″ on each side of the center line 66. The maximumdiameter of each cavity space 92 and 94 is 0.314″, and the maximumdiameter for the spacing channel 96 is 0.174″. Desirably, all surfaceswithin the mold 58 are radiused to provide a smooth transition.

[0072] Prior to heating, one end of the tube length 60 is attached to asource of pressurized air, e.g., nitrogen. The other end of the tubelength 60 is gripped and closed. The tube is desirably subjected to atensioning force (e.g., 16 oz).

[0073] The tube length 60 is then subjected to a heating cycle. Duringthe heating cycle, the tube length 60 is heated to a predeterminedheated temperature for a set dwell time. The heated temperature anddwell time are selected to soften the tube length 60 for subsequentstretching and pressure shaping.

[0074] The range of heated temperatures in which softening occurs willdepend upon the particular composition of the polymeric material used.For example, for the polyurethane tube of the dimensions describedabove, a heated temperature of 290 degrees F. and a dwell time of 220seconds can be used. An operating range of softening temperatures for agiven plastic material can be empirically determined. Suitableprocessing tolerances can also be empirically established.

[0075] When the heating cycle ends, the heat-softened tube length 60 isstretched by pulling it a set amount. The stretching desirably reducesthe thickness of the tube walls. In a representative embodiment, thetube is stretched approximately 0.198″ to each side. The amount ofstretching is selected to facilitate shaping without significantlyreducing the resistance of the material, once shaped, to puncture.

[0076] The mold 58 then closes over the heated and stretched tube length60. Pressurized air (typically, nitrogen) is introduced through theinterior of the tube length 60 for a set amount of dwell time at a setflow rate. The magnitude of pressure, dwell time, and flow rate willvary, depending upon the wall thickness and other physicalcharacteristics of the material used. For the polyurethane tube of thedimensions described, a pressure of 100 PSI at a flow rate of 0.4 l/minfor a dwell time of 45 seconds can be used.

[0077] The introduction of pressurized air into tube length 60 causesthe tube region located within the cavity 64 to expand or billowoutward, forming the structure 56. The cavity 64 limits the extent towhich the structure 56 expands. The structure 56, upon expansion in thecavity 64, will desirably conform to the geometry of the cavity 64.During the pressurization phase, the flow of pressurized air can be usedto help cool the tube length 60.

[0078] After the pressurization phase, the tube length 60 is removedfrom the mold. The source of pressurized air is detached. Excessmaterial on both sides of the formed structure region is discarded.Preferably, at least one inch of tube material is left on each side ofthe formed structure region to aid handling and identification duringfurther processing.

[0079] B. Assembly of the Tool

[0080] 1. Assembling the Outer Catheter Body

[0081] In a representative embodiment, the outer catheter body 16comprises an extruded tube, made from 99% TEXIN® 5270 Material and 1%Titanium Dioxide. The TEXIN® material can be purchased in pellet formfrom Bayer. The outer catheter body can be extruded in a tubular shapeusing, e.g., a screw type (888 4:1) extrusion machine, with a GENCA™head, with a single finger spider and a C5WB23 screen. The followingtable summarizes representative process settings for the extrusion.Extrusion Element Nominal Setting Die 0.203″ Mandrel 0.150″ Zone 1Set/Actual 300 degrees F. Zone 2 Set/Actual 340 degrees F. Zone 3Set/Actual 400 degrees F. Clamp Set/Actual 24.6 degrees F. AdaptorSet/Actual 400 degrees F. Die 1 Set/Actual 400 degrees F. Die 2Set/Actual 400 degrees F. Extruder 400 RPM Motor In. 2300 Auto/Dis. 2929Mandrel Air 5.2 PSI Entry Hole Diameter- 300-½″ Distribution WaterFlow/Temperature 20 ccm Air Wipe 20 PSI Speed 39 FPM Min DryerTime/Temperature Overnight/l60 degrees F.

[0082] The extrusion is initially cut to lengths of 16″ for assembly.

[0083] Each tubing length comprising an outer catheter body 16preferably undergoes annealing, e.g., by oven curing at 60 to 70 degreesC. for 2 to 6 hours. Annealing reduces the incidence of shrinkage of theouter catheter body 16 during sterilization and/or storage prior to use.

[0084] The proximal end of the structure 56 is heat bonded to the distalend of the outer catheter body 16 in the presence of an overlying ringof silicone tubing 68 (see FIG. 5), which compresses the outer catheterbody 16 and the proximal end of the structure 56 together during theheat bonding process. In one representative assembly technique, asupport mandrel (e.g., having an outside diameter of 0.075″) is insertedwithin the outer catheter body 16, and the proximal end of the structure56 is slid over the distal end of the outer catheter body 16. A lengthof the silicone tubing 68 (having, e.g., an initial inside diameter of0.104″) is subsequently slid over the proximal end of the structure 56and the catheter body 16. Heat from the heat box is applied to thesilicone tubing, and the structure and outer catheter body 16 fusetogether. The silicone tubing is then discarded.

[0085] For the materials and dimensions described, representativesettings for the heat box are a temperature of 545 degrees F., an airflow of 40 SCFH, and an air pressure of 20 to 30 PSI. At this setting,the silicone tubing 68 and junction of the structure 56 and the outercatheter body 16 are exposed to heat for 60 seconds, and are rotated 180degrees after the first 30 seconds. The resulting heat bond is allowedto cool.

[0086] The outer catheter body 16 can then be cut to a desired finallength, e.g., which in a representative embodiment is 350 mm measuredfrom the center of the structure 56. In the illustrated embodiment (seeFIG. 4), heat shrink tubing 70, which bears appropriate identificationinformation for the tool 48, is bonded about the outer catheter body 16,about 0.5″ from the proximal end of the outer catheter body 16.

[0087] A suitable UV adhesive (e.g., Dymax 204 CTH, availablecommercially from Dymax Corp) is applied to the proximal end of theouter catheter body 16, and the outer catheter body 16 is inserted intothe handle 14. The adhesive joint is cured under UV light for anappropriate time period, e.g., 15 seconds. This secures the outercatheter body 16 and attached structure 56 to the handle 14.

[0088] 2. Assembling The Inner Catheter Body

[0089] In a representative embodiment, the inner catheter body 18comprises an extruded tube, made from 25% TEXIN® 5286 Material and 75%TEXIN® 5270 Material. The TEXIN® materials can be purchased in pelletform from Bayer.

[0090] The inner catheter body 18 can be extruded in a tubular shapeusing, e.g., a screw type (888 4:1) extrusion machine, with a GENCA™head, with a 80-100-200 screen. The following table summarizesrepresentative process settings for the extrusion. Extrusion ElementNominal Setting Die 0.195″ Mandrel 0.135″ Zone 1 Set/Actual 360 degreesF. Zone 2 Set/Actual 380 degrees F. Zone 3 Set/Actual 490 degrees F.Clamp Set/Actual 400 degrees F. Adaptor Set/Actual 400 degrees F. Die 1Set/Actual 400 degrees F. Die 2 Set/Actual 400 degrees F. Extruder 30.7RPM Motor In. 3300 Auto/Dis. 1772 Mandrel Air 1 PSI Entry HoleDiameter - 300-1″ Distribution Water Flow/Temperature 20 ccm Air Wipe 20PSI Speed 87 FPM Min Dryer Time/Temperature Overnight/160 degrees F.

[0091] The extrusion is initially cut to lengths of 16″ for assembly.Like the outer catheter body 16, the inner catheter body 18 ispreferably subject to heat annealing.

[0092] After annealing, the flared region 52 is formed using a 0.099″stylet heated by a heat gun. One possible setting of the heat gun is 200degrees C. After cooling, UV adhesive is applied to secure the flaredregion 52 to the second luer fitting 34, which, at this stage ofassembly, is not yet connected to the handle 14. The adhesive is curedunder UV light for an appropriate time period.

[0093] In the illustrated embodiment (see FIG. 5), fluoroscopic markerbands 72 are secured on the inner catheter body 18. The marker bands 72facilitate fluoroscopic visualization of the proximal and distal ends ofthe structure 56 on the distal end of the tool 48. In the illustratedembodiment, the marker bands 72 are made from platinum/iridium material(commercially available from Johnson Matthey).

[0094] In a representative embodiment, the marker bands 72 are locatedon the inner catheter body 18 about 1 mm beyond the distal end of theouter catheter body 16 and also distally about 10.6 mm from the centerof the structure 56. Prior to attaching the marker bands 72, the innercatheter body 18 (stiffened by an appropriate interior support mandrel)is inserted into the outer catheter body 16, so that the desiredrelative positions of the marker bands 72 can be determined using areference tool, such as a ruler. The inner catheter body 18 is thenremoved from outer catheter body 16, and the marker bands 72 are affixedat the indicated positions. The distal tip of inner catheter body 18 canbe cut at a 45 degree angle to facilitate slipping the marker bands 72about the body 18. The marker bands 72 are secured to the inner catheterbody 18 using, e.g., a suitable adhesive primer (e.g., Loctite 7701Primer, which is commercially available from Loctite), followed by useof a suitable adhesive (e.g. Cyanoacrylate 4061, which is commerciallyavailable from Loctite). After the adhesive cures, the inner catheterbody 18 is inserted into the outer catheter body 16 and the second luerfitting 34 is secured to the handle 14 using an UV adhesive (e.g.,204-CTH Adhesive, commercially available from Dymax). The adhesive iscured by exposure to UV light for an appropriate time period. Thissecures the inner catheter body 18 to the handle 14.

[0095] The distal end of the inner catheter body 18 can now be securedto the distal end of the structure 56. During this operation, thedimension of the opening 30 of the inner catheter body 18 is alsoreduced, to block passage of the stylet 38, as previously described.

[0096] A first support mandrel (e.g., having an outer diameter of0.041″) is placed within the inner catheter body 18. A temporary ring ofsilicone tubing (e.g., having an inner diameter of 0.132″) is slid overthe junction of the distal end of the structure 56 and the distal end ofthe inner catheter body 18. Using a heat box, heat is applied to thesilicone tubing, which causes the distal end of the stricture 56 toshrink slightly about the inner catheter body 18. This allows a smallerdiameter silicone tubing to be used to form the final bond, as will bedescribed later. Using the materials described, the heat box is set at atemperature of 525 degrees F., an air flow of 30 SCFH, and an airpressure of 20 to 30 psi. Exposure to heat desirably occurs for 16seconds, with the assembly rotated 180 degrees after the first eightseconds.

[0097] The first support mandrel is then removed, and a reduced diameterstylet (e.g., having an outside diameter of 0.008″) is inserted into theinner catheter body 18. A smaller diameter silicone tubing 74 (made,e.g., from silicone tubing having a initial inner diameter of 0.078″)(see FIG. 5) is slid over the junction for final bonding of thestructure 56 to the inner catheter body 18. Heat from theabove-described heat box is then applied for 30 seconds to each side ofthe assembly. The structure-tubing interface is allowed to cool. Thedistal end of the structure 56 is trimmed, e.g., to a 3 mm length.

[0098] As a result of these processing steps, the inside diameter of theopening 30 is desirably reduced to a diameter that approximates theoutside diameter of the reduced diameter stylet (e.g., 0.008″). Thisdiameter is significantly smaller than the outside diameter of thestylet 38, which in the representative embodiment is 0.038″. The reduceddiameter of the opening 30 blocks passage of the stylet 38. Still, thereduced diameter of the opening 30 allows flushing liquid to bedischarged.

[0099] The stylet 38 can now be inserted into the inner catheter body18, with the distal end flush against the distal bond. The proximal endof the stylet 38 is secured by UV-cured adhesive (e.g., 198-M Adhesive,commercially available from Dymax) to the screw cap 50. The cap 50 cannow be screwed upon the second luer fitting 34 of the handle 14.

[0100] A cut length of tubing made of Pebax™ material (e.g., 0.160 inchinterior diameter) is flared at each end, using, e.g., a heat gun with aflare nozzle. This forms the insertion sleeve 54. The insertion sleeve54 is slid over the structure 56 and onto the outer catheter body 16.

[0101] This completes the assembly of the tool 48. The tool 48 can thenbe packaged for sterilization in a suitable kit. If desired, the stylet38 can be packaged next to the tool 48 to facilitate ETO sterilization,and be inserted into the inner catheter body 18 in the manner describedat the time of use.

[0102] III. Use of the Tool

[0103] A. Deployment in a Vertebral Body

[0104] The structure 56 is well suited for insertion into bone inaccordance with the teachings of U.S. Pat. Nos. 4,969,888 and 5,108,404,which are incorporated herein by reference.

[0105] For example, as FIG. 9 shows, access can be accomplished, forexample, by drilling an access portal 76 through a side of the vertebralbody 26. This is called a lateral approach. Alternatively, the accessportal can pass through either pedicle 42, which called a transpedicularapproach. A hand held tool can be used to facilitate formation of theaccess portal 76, such as disclosed in copending U.S. patent applicationSer. No. 09/421,635, filed Oct. 19, 1999, and entitled “Hand HeldInstruments that Access Interior Body Regions.” Another hand held toolthat can be used to form the access portal 76 and gain access isdisclosed in copending U.S. patent application Ser. No. 09/014,229 filedJan. 27, 1998 and entitled “A Slip-Fit Handle for Hand-Held Instrumentsthat Access Interior Body Regions.”

[0106] A guide sheath or cannula 78 is placed into communication withthe access portal 76, which can comprise a component part of the handheld tool just described. The catheter tube assembly 10 is advancedthrough the cannula 78 to deploy the structure 56 into contact withcancellous bone 32. Access in this fashion can be accomplished using aclosed, minimally invasive procedure or with an open procedure.

[0107] The structure 56 is passed into the bone in a normally collapsedand not inflated condition. The presence of the stylet 38 in the innercatheter body 18 serves to keep the structure 56 in the desired distallystraightened condition during its passage through the cannula 78. Theinsertion sleeve 54 is desirably advanced over the structure 56 prior toinsertion into the cannula 78, to protect and compress the structure 56.Once deployed in cancellous bone 32, the stylet 38 can be withdrawn.

[0108] As FIG. 9 shows, expansion of the structure 56 (indicated byarrows in FIG. 9) compresses cancellous bone 32 in the vertebral body26. The compression forms an interior cavity 80 in the cancellous bone32.

[0109] As FIG. 10 shows, subsequent collapse and removal of thestructure 56 leaves the cavity 80 in a condition to receive a fillingmaterial 88, e.g., bone cement, allograft tissue, autograft tissue,hydroxyapatite, or synthetic bone substitute. The material 88 providesimproved interior structural support for cortical bone 32.

[0110] The compaction of cancellous bone 32, as shown in FIG. 9, canalso exert an interior force upon the surrounding cortical bone 28. Theinterior force can elevate or push broken and compressed bone back to ornear its original prefracture, or other desired, condition. In the caseof a vertebral body 26, deterioration of cancellous bone 32 can causethe top and bottom plates (designated TP and BP in FIG. 2), as well asthe side walls (designated AW and PW in FIG. 2), to compress, crack, ormove closer together, reducing the normal physiological distance betweensome or all of the plates. In this circumstance, the interior forceexerted by the structure 56 as it compacts cancellous bone 32 moves someor all of the plates and/or walls farther apart, to thereby restore someor all of the spacing between them, which is at or close to the normalphysiological distance.

[0111] There are times when a lesser amount of cancellous bonecompaction is indicated. For example, when the bone disease beingtreated is localized, such as in avascular necrosis, or where local lossof blood supply is killing bone in a limited area, an expandablestructure 56 can compact a smaller volume of total bone. This is becausethe diseased area requiring treatment is smaller.

[0112] Another exception lies in the use of an expandable structure 56to improve insertion of solid materials in defined shapes, likehydroxyapatite and components in total joint replacement. In thesecases, the structure shape and size is defined by the shape and size ofthe material being inserted.

[0113] Yet another exception lies in the use of expandable structures inbones to create cavities to aid in the delivery of therapeuticsubstances, as disclosed in copending U.S. patent application Ser. No.08/485,394, previously mentioned. In this case, the cancellous bone mayor may not be diseased or adversely affected. Healthy cancellous bonecan be sacrificed by significant compaction to improve the delivery of adrug or growth factor which has an important therapeutic purpose. Inthis application, the size of the expandable structure 56 is chosen bythe desired amount of therapeutic substance sought to be delivered.

[0114] It should be understood that the filling material 88 itself couldbe used to expand the structure 56 within the vertebral body 26, therebycausing compaction of the cancellous bone 32 and/or movement of thecortical bone 28 as previously described. If desired, the fillingmaterial 88 within the structure 56 could be allowed to harden, and thestructure 56 and hardened filling material 88 could remain within thevertebral body 26. This would significantly reduce the possibility ofnon-hardened filling material 88 leaking outside of the vertebral body26. Alternatively, the pressurized fluid could be withdrawn from thestructure 56 after formation of some or all of the cavity 80, and fillermaterial 88 could be injected into the structure to fill the cavity 80and/or complete expansion of the structure 56. As another alternative,filler material 88 could be used to expand the structure 56, and thestructure 56 could subsequently be removed from the vertebral body 26before the filling material 88 within the vertebral body 26 sets to ahardened condition.

[0115] B. Expansion Characteristics of the Structure

[0116] In the illustrated embodiment, the structure 56 is created byextruding or molding a tube 60 of a selected polyurethane material. Thetube 60 is heated, stretched, and subjected to internal pressure. Afterstretching and pressure forming, the tube 60 has a normal wall thickness(T5) and a normal outside diameter (D5) (as shown in FIG. 11).

[0117] The segmented shaped regions 82 and 84 of the structure 56 arecreated by exposing the tube 86 to heat and positive interior pressureinside the cavity 64. Once formed, the structure 56 possesses, in anopen air environment, a normal expanded shape, having diameter D7 (shownin phantom lines in FIG. 11). The normal shape and diameter D7 for theregions 82 and 84 generally correspond with the shape and dimension ofthe cavity spaces 92 and 94, respectively. When an interior vacuum isdrawn, removing air from the structure 56, the structure 56 desirablyassumes a substantially collapsed, and not inflated geometry, shown inphantom lines D6 in FIG. 11.

[0118] The regions 82 and 84 are separated by a tubular waist 86, whichsegments the structure 56 into two expandable regions 82 and 84. Whensubstantially collapsed under vacuum or not inflated, the structure 56desirably exhibits a low profile, ideal for insertion into the cannulaand targeted cancellous bone region.

[0119] The introduction of fluid volume back into the structure 56 willcause each region 82 and 84 to return from the collapsed diameter D6back to the normal, enlarged, but not distended geometry, having theshape and diameter shown in phantom lines D7 in FIG. 11.

[0120] In the illustrated embodiment, the first and second shapedregions 82 and 84 have generally the same radius of expansion and thusthe same non-distended shape and diameter D7. Alternatively, each region82 and 84 can have a different radius of expansion, and thus a differentnon-distended shape and diameter. Moreover, the regions 82 and 84 can beshaped by heat and interior pressure within different cavities to assumedifferent geometries, e.g., cylindrical or elliptical geometry, or anon-spherical, non-cylindrical, or non-elliptical geometry, with eitheruniform or complex curvature, and in either symmetric or asymmetricforms. Of course, more than two segmented regions 82 and 84 can beformed.

[0121] Each shaped region 82 and 84 possesses a wall thickness (designedT7 in FIG. 11) when in the normally enlarged but not distended geometryD7. Due to expansion of the wall during structure formation, the wallthickness is typically not uniform along the longitudinal axis of thestructure 56, i.e., T7 is typically less than the normal wallthicknesses T5 and/or T9 of the tube 60. The wall thickness T7 for theregions 82 and 84 can be the same or different.

[0122] When in the enlarged, but not distended geometry, the waistregion 86 has an outside diameter (designated D9 in FIG. 11), which isdesirably equal to or greater than the diameter D5 of the tube 60. Thesize of the channel 96 in the fixture 90 desirably determines themagnitude of the diameter D9. Due to expansion of the material duringstructure formation, the waist region 86 has a wall thickness(designated T9 in FIG. 11) which is less than or equal to the wallthickness T5 of the tube 60. Desirably, the wall thickness T9 of thewaist region 86 is greater than the wall thickness T7 of either fullyshaped region 82 or 84.

[0123] The formed complex structure 56 thus desirably possesses regionsof non-uniform minimum wall thickness along its longitudinal length;that is, T5, T9>T7. The formed complex structure 56 also providesmultiple expandable regions 82 and 84 of the same or different enlargedoutside diameters (D7), segmented by a waist region 86.

[0124] By injecting additional fluid into the expandable structure 56,the shaped regions 82 and 84 of the structure 56 will desirably continueto enlarge beyond diameter D7 to a distended shape and geometry,designated D8 in FIG. 11. Typically, the wall thickness T7 furtherdecreases and approaches T8. As the regions 82 and 84 expand, the waistregion 86 will likewise expand towards diameter D10, as FIG. 11 shows.However, because the wall thickness T9 of the waist region 86 istypically greater than the wall thickness T7 of the regions 82 and 84,the waist region 86 will typically expand more slowly than the regions82 and 84, thereby expanding the structure 56 in a more cylindricalmanner, providing more uniform, elongated surface contact withcancellous bone than would a spherical expandable structure 56 ofsimilar volume.

[0125] Enlargement of the structure 56 beyond diameter D7 desirablystretches the material in the regions 82, 84, and 86 beyond theirpre-formed geometries. Desirably, these regions 82 and 84 willessentially maintain the preformed shape dictated by the cavities 92 and94. Continued volume flow of pressurized fluid into the structure 56continues to increase the interior volume of the structure 56 (see FIG.12). As their volume increase, the shaped regions 82 and 84 of thestructure 56 continue to enlarge beyond the normal diameter D7 toward adistended shape and geometry D8.

[0126] Of course, it should be understood that the waist region 86 couldbe formed of a material having different expansion characteristics thanthe material of the shaped regions 82 and 84, wherein a moreexpansion-resistant material could constrain the expansion of the waistregion in a manner similar to the thickness differentials describedabove.

[0127] The degree of stretching and increases in volume can be tailoredto achieve a desired, fully distended diameter D8. The final, fullydistended diameter D8 can be selected by the treating physician, usingreal-time monitoring techniques, such as fluoroscopy or real-time MRI,to match the dimensions of the targeted cancellous bone region. Thecontrolled stretching of the segmented regions 82 and 84 desirablyprovides compression of cancellous bone with a maximum diameter that isless than a single non-segmented region (i.e., one without the waistregion 86). Stated another way, segmented regions 82 and 84, whenexpanded to a given inflation volume, desirably have an outer diameterless than a sphere expanded to an equal inflation volume.

[0128] While expanding in the region between D7 and D8, the structure56, when inside bone, desirably assumes an increasingly larger surfaceand volume, thereby compacting surrounding cancellous bone. Inflation incancellous bone may occur at the same pressures as outside bone.However, an increase in the inflation pressures inside bone may berequired, due to the density of the cancellous bone and resistance ofthe cancellous bone to compaction.

[0129] For example, the configuration of the Pressure vs. Volume curvefor a given material and structure 56 remains essentially the same asshown in FIG. 12, except that the generally horizontal portion of thecurve between D7 and D8 is shifted upward on the Y-axis, as shown inphantom lines in FIG. 12. As a general statement, the threshold pressureinside bone is determined by the material property of the structure 56and any added resistance due to the presence of cancellous bone.

[0130] The distance between D7 and D8, along the x-axis of FIG. 12,defines the degree to which the wall can elongate at a substantiallyconstant pressure condition and with increasing material stress tocompact cancellous bone, without failure. As volume increases at thesubstantially constant threshold pressure P(t), wall failure becomesmore likely as the diameter of the structure enlarges significantlyfurther beyond the distended diameter D8. There comes a point when thestructure 56 can no longer increase its volume as the materialelasticity approaches ultimate elongation, or as material stressapproaches ultimate tensile strength. When either of these ultimatevalues are reached, wall failure is likely. Accordingly, the distancebetween D7 and D8 in FIG. 12 during expansion inside bone is asimultaneous expression of the three physical and mechanicalproperties—expansion, shape, and toughness—as previously described.

[0131] The features of the invention are set forth in the followingclaims.

We claim:
 1. A tool for deploying an expandable structure into interiorbody regions, the tool comprising a catheter body defining an interiorlumen, an expandable structure having a distal end and carried by thecatheter body, and a stylet having a proximal end and being sized andconfigured for passage through the lumen and adapted to straighten theexpandable structure during deployment into an interior body region. 2.A tool as in claim 1 wherein the stylet is substantially rigid.
 3. Atool as in claim 1 wherein the stylet is made of stainless steel.
 4. Atool as in claim 1 wherein, after passage of the stylet through thelumen, the proximal end of the stylet is coupleable to the catheterbody.
 5. A tool as in claim 1 wherein, after passage of the styletthrough the lumen, the stylet abuts against the distal end of theexpandable structure.